Housing for diverse cooling configuration printed circuit cards

ABSTRACT

A printed circuit card housing provides separate cooling fluid travel paths for convectively cooling on-board heat exchangers of non mil. spec. component-retaining printed circuit cards, and for thermal conductive cooling of conventional (VME) circuit cards, while keeping both types of circuit cards sealed from contaminants that may be present in the cooling fluid. The housing includes a chassis having a card slot cavity, into which both types of printed circuit cards are retained. A cooling fluid supply/exhaust plenum provides a first cooling fluid travel path that is ported to only convectively cooled circuit cards. In order to cool the remaining circuit cards, the cooling fluid supply/exhaust plenum ports cooling fluid entering the plenum along a second cooling fluid travel path through heat exchangers installed along sidewalls of the chassis.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of Ser. No. 08/916,831, filedAug. 22, 1997 now U.S. Pat. No. 5,982,619, which is acontinuation-in-part of application, Ser. No. 08/873,677, filed Jun. 12,1997, now U.S. Pat. No. 5,835,349, entitled: "Printed CircuitBoard-Mounted, Sealed Heat Exchanger," by C. Giannatto et al(hereinafter referred to as the '677 application), assigned to theassignee of the present application and the disclosure of which isherein incorporated.

FIELD OF THE INVENTION

The present invention relates in general to a housing and coolingenclosure for securely retaining and cooling a multiple types of printedcircuit cards. In particular, the housing and cooling enclosure of theinvention provides parallel circulation paths for a cooling fluidthrough cooling fluid flow chambers of on-board heat exchangers ofconvectively cooled printed circuit cards, and through thermallyconductive heat exchangers along sidewalls of a chassis for thermallyconductively cooled printed circuit cards.

BACKGROUND OF THE INVENTION

As described in the above-referenced '677 application, a variety ofcommunication systems, particularly those installed in mobile (e.g.,land-based) platforms, are designed to be environmentally robust interms of their hardware and signaling format. As a non-limiting example,for the case of a vehicle-mounted, communication system intended for usewith a plurality of UHF line-of-sight and satellite links, a multi-linktransceiver mounting rack may contain a plurality of diverse pieces ofcommunication equipment, that typically include RF transmitter modules,RF receiver modules, and various digital signal processing modules,which control the operation of the RF components, and interface digitalcommunications signals with attendant encryption and decryptionprocessing circuits. Since each communication link has its own dedicatedsignalling scheme (modulation format, link protocol, band occupancyassignment, etc.), suppliers of such equipment will typically provideeach system as an integrated unit.

One of the standard bus architectures employed for such systems is theVME bus, which is comprised of a pair of multiple lead bus links. One ofthese bus links has a predefined set of bus connection definitions, towhich each module that may be plugged into the VME bus must conform. Onthe other hand, other than limited power rail assignments, the secondbus link has unspecified bus connection definitions, allowing the userto customize the second bus link, or connector interconnects to that buslink, as desired.

Typically, RF signaling circuits and digital signaling modules plug intotheir own connector slots on the VME bus, in order to providenoise/cross-talk isolation between the RF and digital signal processingcomponents of a given communication system architecture, and to conformwith the relatively tight (center-to-center) dimensional spacingsbetween connector slots on the VME bus. Signal connections betweenmodules may be effected by cabling links between the modules and/or useone or more pins of module connectors for the second bus link portion ofthe VME bus, connection definitions for which would otherwise beunspecified for user customization.

Because VME-based communication system platforms can be expected to beemployed in relatively harsh environments that expose the platforms tovibration, foreign matter and potentially damaging temperaturevariations, VME bus specifications mandate ruggedized housingarchitectures, that also cool the circuit components and effectivelyseal them from the external ambient. To accomplish these objectives ithas been conventional practice to use very complex (and expensive)chassis-integrated heat transfer structures, on the one hand, and to usemore thermally robust circuit components, per se, which undesirably addsubstantial bulk (and cost) to each circuit board, and thus to theoverall housing assembly.

Advantageously, the printed circuit card support and coolingarchitecture described in the above-referenced '677 application, anddiagrammatically illustrated in FIG. 1, is configured to remedy suchshortcomings of conventional (VME) bus-mounted communication signalprocessing module configurations, by reducing the heat resistance pathsto within a thermal parameter window that allows the use of commercialgrade printed circuit card components. Moreover, its housingarchitecture has a smaller size than a conventional thermally controlledVME bus-based communication system architecture, so as to facilitateinstallation of a VME bus-based signal processing system configurationin a relatively limited volume hardware platform.

In particular, the housing structure of the '677 application has agenerally regular rectangular, metallic chassis 10 formed of first andsecond parallel sidewalls 11 and 13, that adjoin parallel end walls 15and 17, that are generally orthogonal to the sidewalls, and definetherebetween a generally rectangular card-insertion cavity 21. Thebottom of the chassis 10 is closed by a bottom cover 23, while the topis closed by a top cover 25.

The card insertion cavity 21 is bounded by a pair of slotted frames 27,which contain generally vertical, card-guide slots 29, that are sized toreceive guide posts 31 mounted to opposite side edges 33 and 35 ofrespective printed circuit cards 40. At the bottom of the slotted frames27 is a connector retention plate 37, supporting a parallel arrangementof spaced-apart, multi-pin electrical connectors 41. The multi-pinconnectors receive associated dual in-line multi-pin connectors 43attached to bottom edges 45 of the circuit cards 40, so that wheninstalled in the chassis, the circuit cards are securely retained inmutually adjacent, spatially parallel relationship.

As shown in greater detail in the exploded views of FIGS. 2 and 3, andin the top view of FIG. 4 and the front view of FIG. 5, in order to coola respective circuit card 40, a generally frame-configured, thermallyconductive (e.g., metallic), convection-based heat exchanger 50 ismounted to one side 53 of the card, and functions to draw heat away fromcircuit components 42 on a second side 55 of the card. Affixing the heatexchanger 50 directly to the printed circuit card also increases theflexure stiffness of the card; mounting the circuit components 42 andheat exchanger 50 on opposite sides of the card 40 isolates the circuitcomponents from the heat exchanger, preventing the circuit componentsfrom being exposed to any potentially corrosive foreign matter that maybe present in the cooling fluid (typically external ambient air) flowingthrough the card's on-board heat exchanger.

The heat exchanger 50 has the general configuration of a frame 60 that atop wall 61, sidewalls 63 and 65, a bottom wall 67, and a back wall 68.These walls of a generally rectangular heat exchanger frame 60 form acooling fluid flow chamber 70, containing adjacent, generallyrectangular cooling fluid flow chamber sections 71 and 73, which areported by cooling fluid inlet and exhaust ports 81 and 83 formed withinthe frame's top wall 61. The heat exchanger frame 60 also has a centerwall 69, that extends from the top wall 61 to a location 75 spaced apartfrom the bottom wall 67, so as to form an intra chamber fluidcommunication port 85 connecting fluid flow chamber sections 71 and 73.A cover plate 80 is secured to the walls of the frame and thereby formsa front wall for the heat exchanger. The heat exchanger frame 60 and itsadjoining cover plate 80 are sized to conform with the printed circuitcard 40, so that when the cover plate 80 is surface-joined with thefirst side 53 of the circuit card 40, the entirety of the card surfacearea upon which the card's circuit components 42 are mounted isthermally coupled to the heat exchanger 50.

This direct face-to-face thermal coupling between the entirety of thefirst side 53 of the circuit card 40 with cover plate 80 reduces thelength of the thermal resistance path between any circuit component 42and the heat exchanger 50. It also causes the average temperature at anypoint on the printed circuit card 40 to be uniformly the same, resultingin the lowest possible component temperatures for any given material setand cooling fluid conditions. As a consequence, circuit components 42mounted to the second side 55 of printed circuit card 40 need not bemil-spec; instead, commercial grade circuit elements, which areconsiderably less costly, may be used.

The circuit card's on-board heat exchanger 50 further includes first andsecond thermally conductive, fin-shaped corrugated heat exchangerelements 91 and 93 retained in respective chamber sections 71 and 73 ofthe cooling fluid flow chamber 70. These fin-shaped corrugated heatexchanger elements 91 and 93 are sized to substantially fill chambers 71and 73, but leave a fluid circulation region 79 between bottom edges 92and 94 of elements 91 and 93, respectively, and the bottom wall 67 ofthe frame 60. This fluid circulation region 79 serves as a return pathfor cooling fluid that has entered the chamber 71 via inlet port 81 andhas traveled (downwardly, as shown at arrows 96) through heat exchangerelement 91.

Upon exiting the bottom of heat exchanger element 91 in chamber 71, thecooling fluid then travels through the intra chamber fluid communicationport 85 of region 79 and enters the bottom of heat exchanger element 93in chamber 73. The cooling fluid then travels (upwardly as shown byarrows 98) through heat exchanger element 93 and exits chamber 73through cooling fluid exhaust port 83. Advantageously, since eachcooling fluid port 81 and 83 is located in a plane (top wall 61) that isparallel to the circuit card 40, the effective thickness of theintegrated heat exchanger--printed circuit board architecture of the'677 application is such as to allow the circuit card to be readilyinserted into any of the connectors 41 of the chassis 10.

In order to supply and remove cooling fluid via the ports 81 and 83, acooling fluid supply/exhaust plenum 100 is mounted to a top portion 12of the chassis 10. The plenum 100 includes a cooling fluid supplychamber 101 and a cooling fluid removal chamber 103 that are in fluidcommunication with the chambers 71 and 73 of the thermally conductiveheat exchangers 50 of respective ones of printed circuit cards 40. Theplenum 100 includes a generally rectangular frame 110 defined by a firstsidewall 111, an end wall 113, a second sidewall 115, and a bottom wall117, that generally enclose the pair of adjacent, generally rectangularchambers 101 and 103. Chamber 101 serves as a cooling fluid supplychamber and has a cooling fluid supply port 121 formed in a cover 120that is attached to the top edges of the walls of frame 110.Complementarily, chamber 103 serves as a cooling fluid removal chamberand has a cooling fluid removal port 123 defined by a plenum opening 114along a side portion 118 of the frame 110 coincident with an opening inthe chassis 10.

The plenum frame 110 has a center wall 119 that extends from the firstsidewall 111 to the second sidewall 115, so as to isolate the plenumchambers 101 and 103 from each other. Within the plenum chamber 101, thebottom wall 118 has a first set of generally elongated slots 131. Slots131 are coincident with and adjoin the fluid inlet ports 81 ofrespective heat exchangers 50 of the circuit cards 40, when the cardsare retained in their associated chassis guide slots. The floor portionof the plenum chamber 103 also has a second set of generally elongatedslots 133, coincident with and adjoining the fluid exhaust ports 83 ofthe respective heat exchangers 50, when the cards are retained in theirguide slots.

To seal the cooling fluid interfaces between slots 131 and 133 of plenum100 and the fluid inlet and exhaust ports 81 and 83 of the heatexchangers 50, a multi-slotted gasket 140 is installed between the floor118 of the plenum 100 and the top walls 61 of the heat exchanger frames60. The gasket 140 has sets of generally elongated slots 141 and 143,that are coincident with and adjoin the elongated slots 131 and 133 ofthe plenum 110, and thereby the respective fluid inlet and exhaust ports81 and 83 of the heat exchangers 50. What results is a cooling fluidpath that is convectively coupled with each printed circuit card, yet issealed off from their components, so that contaminants, which might bepresent in the cooling fluid (e.g., ambient air drawn in from theoutside of the chassis), cannot come in contact with the circuitcomponents of the printed circuit cards.

Now although the improved printed circuit card-mounted heat exchangerarchitecture described in the above-referenced '677 application isconfigured to convectively cool the components of the printed circuitcards using the outside ambient, while at the same time sealing thecooled components from the ambient medium, per se, there arecircumstances where it is desired to employ standard VME circuit cards(which are cooled by thermally conducting paths interfacing the sides ofthe cards) in the same housing. Thus, there is a need for a housingconfiguration which will accommodate and cool both types of circuitcards--those that use less restrictive tolerance (e.g., non mil spec.)components, and those employing mil. spec. tolerance components.

SUMMARY OF THE INVENTION

In accordance with the present invention, this desire is successfullyaddressed by an efficient hardware modification of the housing andcooling architecture described in the above-referenced '677 application,that provides parallel cooling fluid travel paths for convective coolingof on-board heat exchangers of the non nil spec circuit cards, and forthermal conductive cooling of conventional (VME) circuit cards, whilekeeping both types of circuit cards protected from contaminants that maybe present in the cooling fluid. For this purpose, like the housing andcooling architecture described in the above-referenced '677 application,the parallel cooling path housing structure of the present inventionincludes a chassis having a card-insertion cavity, into which on-board,convectively cooled printed circuit cards of the type described in the'677 application may be inserted and retained in mutually adjacent,spatially separated relationship.

However, rather than being ported to each of the card slots of thehousing, the cooling fluid supply/exhaust plenum for the card-insertioncavity provides a first cooling fluid path that is ported to only aselected number of the card slots, in particular only those card slotsfor convectively cooled circuit cards of the type described in the '677application. A multi-slotted gasket is inserted between the plenum floorand the cards' on-board heat exchangers, thereby sealing the coolingfluid interfaces between the plenum floor slots and the fluid inlet andexhaust ports of the cards' heat exchangers.

This ensures that the cooling fluid path for the convectively cooledcards is integrally thermally coupled with each such circuit card, yetis sealed off from the components mounted on the circuit cards, so thatany potential contaminants in the cooling fluid cannot come in contactwith either the convectively cooled printed circuit cards, or theremaining circuit cards at whose card positions no slots are provided inplenum floor. In order to cool the remaining circuit cards, the coolingfluid supply/exhaust plenum is configured to port cooling fluid enteringthe plenum along a second cooling fluid path through heat exchangersinstalled along sidewalls of the chassis, which are thermallyconductively coupled to the sides of the cards.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a printed circuit card supportand cooling structure described in the above-referenced '677application;

FIG. 2 is an exploded perspective view showing details of components ofthe structure of FIG. 1;

FIG. 3 is a reverse exploded perspective view of a printed circuit cardand heat exchanger of FIGS. 1 and 2;

FIG. 4 is a top view of a heat exchanger frame;

FIG. 5 is a front view of a heat exchanger frame, showing heat exchangerelements installed in cooling chambers of the frame;

FIG. 6 is a front exploded perspective view of a dual cooling path,printed circuit card support and cooling structure in accordance withthe present invention;

FIG. 7 is an open top view of dual cooling path, printed circuit cardsupport and cooling structure of FIG. 6; and

FIGS. 8, 9, 10 and 11 are respective front, rear, side and top views ofthe dual cooling path, printed circuit card support and coolingstructure of FIGS. 6 and 7.

DETAILED DESCRIPTION

Like the housing structure of the '677 application, the dual coolingpath, printed circuit card support and cooling architecture of thepresent invention, diagrammatically illustrated in FIGS. 6-11, comprisesa generally regular rectangular, six-sided, ruggedized metallic chassis210 having first and second parallel sidewalls 211 and 213, which adjoina front panel/endwall 215 and an interior rear endwall 217,respectively, that are generally orthogonal to the chassis sidewalls,and define a generally rectangular printed circuit card-insertion cavitytherebetween. The front panel/endwall 215 is fitted with variousconnectors and control elements, as shown.

The interior rear endwall 217 is spaced apart from a back cover 219,that also intersects sidewalls 211 and 213, forming the rear extremityof the housing and defining a cooling fluid supply space 218 between theinterior rear endwall 217 and the housing's back cover 219. A pair ofspaced apart vertical walls 222 and 224 are formed between and adjoineach of the interior rear endwall 217 and the housing's back cover 219,so as to subdivide the cooling fluid supply space 218 into threepockets, comprising a central, cooling fluid inlet pocket 226, and apair of side supply pockets 228 and 229. The cooling fluid inlet pocket226 is ported to the external ambient via an aperture 232 formed in acircular plate 233 that is mounted to and forms part of the back cover219.

The card-insertion cavity is bounded by a pair of mutually oppositeslotted frames 227, which contain a first set of generally vertical,card-guide slots 234, that are spaced and sized to receive the guideposts 31 on opposite side edges 33 and 35 of respective convective heatexchanger-containing printed circuit cards 40, configured asdiagrammatically illustrated in FIG. 3-5, described above. Frames 227additionally contain a second set of generally vertical, card-guideslots 236, that are spaced and sized to receive guide posts 32 onopposite side edges 34 and 36 of respective ones of conventionallyconfigured, thermally conductively cooled printed circuit cards 44.

At the bottom of the slotted frames 227 is a connector retention plate237, which supports a parallel arrangement of spaced-apart, multi-pinelectrical connectors 238. These multi-pin connectors receive dualin-line multi-pin connectors, that are attached to the bottom edges ofthe circuit cards 40 and 44, so that, when installed in the chassis 210,both types of circuit cards are retained in their intended mutuallyadjacent, spaced-apart parallel relationship. A housing bottom cover 220is secured (as be screws 235) to the bottom of the chassis 210 beneathconnector retention plate 237.

In order to supply and remove cooling fluid to and from each of theon-board, convective heat exchangers 50 of the circuit cards 40, acooling fluid supply and removal plenum 200 is installed immediatelyadjacent to a top portion of the chassis 210. The cooling fluid plenum200 includes a cooling fluid injection chamber 201 and a cooling fluidremoval chamber 203, that are ported via a plurality of elongated slots241 and 243, respectively, to heat exchanger chambers 71 and 73 of eachthermally conductive heat exchanger 50 of a respective convectivelycooled printed circuit card 40.

The cooling fluid plenum 200 is configured as a generally rectangularframe defined by first and second sidewalls 251 and 253, first andsecond end walls 255 and 257, and a floor or bottom wall 259, thatencompass the chambers 201 and 203. The geometries of the respectivecooling fluid injection and removal chambers 201 and 203 of the coolingfluid plenum 200 are further defined by a center wall 261, a first end263 of which terminates at a first interior endwall 265, that extends tothe first sidewall 251. A second end 267 of the center wall 261terminates at a second interior endwall 269, which extends to the secondsidewall 253.

A cooling fluid inlet port 271 is formed in a first end region of thefloor 259 between the first interior endwall 265 and endwall 257. Firstand second cooling fluid outlet ports 275 and 276 are formed in secondand third respective end regions of the plenum floor 259, adjacent toopposite sides of the cooling fluid inlet port 271. The plenum's centerwall 261 and connected interior end walls 265 and 269 isolate thecooling fluid inlet and removal chambers 201 and 203 of the plenum 200from each other.

Within the cooling fluid inlet chamber 201, the first set of generallyelongated slots 241 are coincident with and adjoin the fluid inlet ports81 of respective on-board heat exchangers 50 of the convectively cooledcircuit cards 40, when the cards 40 are retained in their associatedchassis guide slots. Also, the second generally elongated slots 243 arecoincident with and adjoin the fluid exhaust ports 83 of the respectiveheat exchangers 50 of the circuit cards 40 as retained in theirrespective guide slots.

A multi-slotted gasket 282 is inserted between the plenum floor 259 andthe top walls 61 of the heat exchanger frames 60 of the heat exchangers50, so as to seal the cooling fluid interfaces between slots 241 and 283of the plenum chambers 201 and 203 and the fluid inlet and exhaust ports81 and 83 of heat exchangers 50. This ensures that the convectivecooling fluid path for the cards 40 is integrally thermally coupled witheach printed circuit card 40, yet is sealed off from the components 42mounted on the printed circuit cards 40, so that any potentialcontaminants, which might be present in the cooling fluid (ambient airdrawn in from outside the chassis 210), cannot come in contact witheither the convectively cooled printed circuit cards 40 or the thermallyconductively cooled circuit cards 44, at whose card positions no slotsare provided in the plenum floor.

A thermally conductive plenum cover 260, having a cooling fluid exhaustaperture 270 adjacent to the plenum endwall 255, is affixed to the topsurface of the plenum 200, closing cooling fluid chambers 201 and 203and the top of the housing. The first cooling fluid outlet port 275 ofthe plenum floor 259 is ported through a first sidewall aperture 272 atthe side supply pocket 229, to a chamber 293 of a first sidewall heatexchanger 290, affixed to a first side 214 of the chassis 210. In a likemanner, the second first cooling fluid outlet port 276 of the plenumfloor 259 is ported through a second sidewall aperture at the sidesupply pocket 228, to a chamber of a second sidewall heat exchanger 300affixed to a second side 216 of the chassis 210.

Chamber 293 of the first sidewall heat exchanger 290 has an elongatedslot-configured cooling fluid exhaust port 295 formed in frontendwall/panel 215 of the chassis 210. A thermally conductive,fin-shaped, generally elongated corrugated heat exchanger element 296 isinstalled in chamber 293, so as to be in intimate thermal contact withthe thermally conductive sidewall surface 294 of sidewall chamber 293.In like manner, chamber 303 of the second sidewall heat exchanger 300has an elongated slot-configured cooling fluid exhaust port 305 formedin the chassis' front endwall 215. Also, a thermally conductive,fin-shaped, generally elongated corrugated heat exchanger element 306 isinstalled in the chassis' opposite sidewall chamber, so as to be inintimate thermal contact with the thermally conductive sidewall surfaceof that sidewall chamber. The respective sidewall chambers of thechassis 210 are closed by chassis sidewall covers 297 and 307.

In operation, cooling fluid (external ambient air) enters the coolingfluid inlet pocket 226 through the aperture 232 in the chassis' backcover 219, and travels upwardly through cooling fluid inlet port 271 inthe cooling fluid plenum floor 259. A first portion of the air passingthrough the cooling fluid inlet port 271 travels along a firstconvective path into the cooling fluid inlet chamber 201, while a secondportion of the air travels along a second path for the conductivelycooled cards 44, to the first and second cooling fluid outlet ports 275and 276.

The air traveling along the first cooling fluid trave path and enteringthe plenum's cooling fluid inlet chamber 201 then travels into the firstset of generally elongated slots 281 in the plenum's floor 259 and intothe fluid inlet ports 81 of respective on-board heat convectiveexchangers 50 of the convectively cooled circuit cards 40. Cooling fluidthat has circulated through the cards' convective heat exchangers 50 isreturned upwardly through the slots 283 of the fluid removal chamber203, and exits the plenum 200 through the cooling fluid exhaust aperture270 in the plenum cover 268.

As noted earlier, the slots 281 and 283 in the plenum floor 259 overlieonly those card slots where convectively cooled circuit cards 40, havingon-board, convective heat exchangers 50, are installed. Moreover theseslots are sealed by means of the multi-slotted gasket 282 insertedbetween the plenum floor 259 and the top walls 61 of the heat exchangerframes 60 of the heat exchangers 50. Thus, the convective cooling fluidpath for the circuit cards 40 is integrally thermally coupled with eachprinted circuit card 40, per se, yet physically sealed off from thecomponents 42 mounted on the printed circuit cards 40. This prevents anypotential contaminants in the cooling fluid (ambient air drawn in fromoutside the chassis 210) from coming in contact with either theconvectively cooled printed circuit cards 40, or the thermallyconductively cooled circuit cards 44 (at whose card positions no slotsare provided in the plenum floor 259).

The air traveling along the second cooling fluid travel path andentering the first and second cooling fluid outlet ports 275 and 276passes through side supply pockets 228 and 229 and is ported throughsidewall apertures 272 and 274 to respective sidewall heat exchangers290 and 300. The cooling air then passes through the heat exchangerelements 296 and 396 installed in the respective sidewall chambers ofthe chassis, removing heat thermally transferred thereto through thechassis sidewalls from the circuit cards 44, and exits the housingthrough the exhaust ports 295 and 305 at the sides of the front panel215. Since the entirety of the card insertion cavity (for both cards 40and 44) is sealed from the second path cooling air, any contaminants inthe second path cooling fluid cannot come in contact with either type ofcard installed in the card insertion cavity.

As will be appreciated from the foregoing description, through anefficient hardware modification of the housing and cooling architecturedescribed in the above-referenced '677 application, the presentinvention provides a dual card type support and cooling enclosure,having parallel cooling fluid travel paths emanating from a singlecooling fluid inlet port, that affords convective cooling of bothprinted circuit cards employing on-board heat exchangers, and thermalconductive cooling of conventional (VME) circuit cards, that areinstallable in the same (VME) bus.

While we have shown and described an embodiment in accordance with thepresent invention, it is to be understood that the same is not limitedthereto but is susceptible to numerous changes and modifications as areknown to a person skilled in the art, and we therefore do not wish to belimited to the details shown and described herein, but intend to coverall such changes and modifications as are obvious to one of ordinaryskill in the art.

What is claimed:
 1. A method of securely retaining and cooling within asealed housing enclosure both convectively cooled printed circuit cardsand conductively cooled printed circuit cards, said method comprisingthe steps of:(a) providing a chassis having a sealed card-insertioncavity between parallel sidewalls thereof, containing a plurality ofcard-guide slots that are configured to receive and guide saidconvectively cooled printed circuit cards and said conductively cooledprinted circuit cards into electrical connectors arranged parallel withone another at a first portion of said chassis; (b) mounting thermallyconductive sidewall heat exchangers at sidewalls of said chassis andover which cooling fluid passes, said thermally conductive sidewall heatexchangers being thermally conductively coupled to said conductivelycooled printed circuit cards through sidewalls of said chassis so as tothermally remove heat therefrom through said chassis sidewalls; (c)providing a cooling fluid supply/exhaust plenum at a second portion ofsaid chassis, that is spaced apart from said first portion of saidchassis and sealing said card-insertion cavity therebetween, saidcooling fluid supply/exhaust plenum including a cooling fluid supplychamber having a plurality of cooling fluid supply apertures overlyingcard slots of only said convectively cooled printed circuit cards, and acooling fluid exhaust chamber adjacent to said cooling fluid supplychamber and from which said cooling fluid having cooled circuitcomponents of said convectively cooled printed circuit cards is removed,said cooling fluid exhaust chamber having a plurality of cooling fluidremoval apertures adjacent to said plurality of cooling fluid supplyapertures; (d) attaching a plurality of thermally conductive heatexchangers to first sides said convectively cooled printed circuitcards, such that a respective thermally conductive heat exchanger isattached to and in thermally conductive engagement with a first side ofa respective convectively cooled printed circuit card, and is operativeto draw heat away from and thereby cool said circuit components that aremounted to a second side of said respective convectively cooled printedcircuit card, said respective thermally conductive heat exchangerincluding a cooling fluid inlet port joined in sealing engagement with arespective cooling fluid supply aperture of said plurality of coolingsupply apertures of said cooling fluid supply chamber of said coolingfluid supply/exhaust plenum, and through which said cooling fluid isintroduced from said cooling fluid supply/exhaust plenum, and a coolingfluid outlet port adjacent to said cooling fluid inlet port and joinedin sealing engagement with a respective cooling fluid removal apertureof said plurality of cooling fluid removal apertures of said coolingfluid exhaust chamber of said cooling fluid supply/exhaust plenum, andthrough which said cooling fluid is exhausted from said heat exchangerinto said cooling fluid supply/exhaust plenum; (e) installing saidconvectively cooled printed circuit cards and said conductively cooledprinted circuit cards into said arrangement of electrical connectors, sothat said convectively cooled printed circuit cards and saidconductively cooled printed circuit cards are retained thereby inmutually adjacent, spatially parallel relationship with one another; and(f) supplying cooling fluid to said cooling fluid supply chamber so thatsaid cooling fluid flows through said plurality of cooling fluid supplyapertures overlying card slots of only said convectively cooled printedcircuit cards, through said plurality of thermally conductive heatexchangers attached to said first sides said convectively cooled printedcards and exits by way of said plurality of cooling fluid removalapertures of said cooling fluid exhaust chamber.
 2. A method accordingto claim 1, wherein said conductively cooled printed circuit cardscomprise VME circuit cards, and wherein step (b) comprises interfacingsaid VME circuit cards by way of thermally conducting paths to saidthermally conductive sidewall heat exchangers mounted at said sidewallsof said chassis, and wherein said convectively cooled printed circuitcards contain commercial grade printed circuit card components havingtolerance restrictions less than printed circuit card components of saidVME circuit cards.
 3. A method according to claim 1, wherein saidrespective thermally conductive heat exchanger further includes a framehaving a first end wall adjoining said fluid supply/exhaust plenum andcontaining said cooling fluid inlet port and said cooling fluid outletport, sidewalls parallel with side edges of said convectively cooledprinted circuit cards, a second end wall opposite to said first endwall, and a back wall, that enclose first and second adjacent coolingfluid flow chambers, and a further wall that extends from said first endwall to a location spaced apart from said second end wall, so as toprovide an intra chamber fluid communication port connecting said firstand second cooling fluid flow chambers, and a heat exchanger coverplate, and wherein said heat exchanger further includes first and secondthermally conductive heat exchange elements, respectively retained inand substantially filling said first and second cooling fluid flowchambers, but leaving a fluid circulation region therein that provides afluid flow loop path for cooling fluid that has entered said firstchamber via said cooling fluid inlet port in said first end wall of saidframe, and has traveled through said first heat exchange element and,upon exiting said first heat exchange element, travels through saidfluid circulation region and said second heat exchange element in saidsecond chamber, exiting through said cooling fluid exhaust port in saidfirst end wall of said frame.
 4. A method according to claim 1, whereinstep (c) further includes providing gasket material that forms a sealedinterface between said cooling fluid supply and removal slots of saidsupply/exhaust plenum and said cooling fluid inlet and exhaust ports,respectively, of said thermally conductive heat exchangers.
 5. A methodaccording to claim 4, wherein said gasket material comprises amulti-apertured gasket inserted between said supply/exhaust plenum andsaid first end wall of said heat exchanger.
 6. A method according toclaim 1, wherein step (a) includes configuring said chassis with acooling fluid inlet that is ported to external ambient and is configuredto supply cooling fluid to said cooling fluid supply/exhaust plenum. 7.A method according to claim 6, wherein said sidewalls of said chassisinclude respective chambers that are ported to said cooling fluidsupply/exhaust plenum at a first portion of said chassis adjacent to afirst end of said sidewalls of said chassis, and are ported to externalambient at a second portion of said chassis adjacent to a second end ofsaid sidewalls of said chassis, said respective chambers containingthermally conductive heat exchanger elements that are thermallyconductively coupled through said chassis sidewalls to said conductivelycooled printed circuit cards and over which cooling fluid passes as ittravels through said chambers.
 8. A method of securely retaining andcooling first and second, respectively diverse types of printed circuitcards in a housing comprising the steps of:(a) providing a chassishaving a card-insertion cavity between sidewalls thereof, and containinga plurality of card slots having electrical connectors at a firstportion of said chassis that retain said first and second, respectivelydiverse types of printed circuit cards in mutually adjacent, spatiallyparallel relationship with one another; (b) providing a cooling fluidsupply/exhaust plenum for said first type of printed circuit boards at asecond portion of said chassis spaced apart from said first portion ofsaid chassis and sealing said card-insertion cavity therebetween, saidcooling fluid supply/exhaust plenum including a cooling fluid supplychamber, to which cooling fluid for convectively cooling circuitcomponents of said first type of printed circuit cards is supplied, saidcooling fluid supply chamber having a plurality of cooling fluid supplyapertures overlying card slots of only said first type of printedcircuit cards, and a cooling fluid exhaust chamber adjacent to saidcooling fluid supply chamber and from which said cooling fluid havingcooled circuit components of said first type of printed circuit cards isremoved, said cooling fluid exhaust chamber having a plurality ofcooling fluid removal apertures adjacent to said plurality of coolingfluid supply apertures; (c) attaching a plurality of thermallyconductive heat exchangers to said first type of printed circuit cards,such that a respective thermally conductive heat exchanger is attachedto and in thermally conductive engagement with a first side of arespective first type of printed circuit card, so as to draw heat awayfrom and thereby cool said circuit components mounted to a second sideof said respective first type of printed circuit card, and wherein saidrespective thermally conductive heat exchanger includes a cooling fluidinlet port joined in sealing engagement with a respective cooling fluidsupply aperture of said plurality of cooling supply apertures of saidcooling fluid supply chamber of said cooling fluid supply/exhaustplenum, and through which said cooling fluid is introduced from saidcooling fluid supply/exhaust plenum, and a cooling fluid outlet portadjacent to said cooling fluid inlet port and joined in sealingengagement with a respective cooling fluid removal aperture of saidplurality of cooling fluid removal apertures of said cooling fluidexhaust chamber of said cooling fluid supply/exhaust plenum, and throughwhich said cooling fluid is exhausted from said heat exchanger into saidcooling fluid supply/exhaust plenum; (d) mounting thermally conductivesidewall heat exchangers for cooling said second type of printed circuitcards and being mounted at sidewalls of said chassis and over whichcooling fluid passes, said thermally conductive sidewall heat exchangersbeing thermally conductively coupled to said second type of printedcircuit cards through sidewalls of said chassis so as to thermallyconductively remove heat therefrom through said chassis sidewalls; and(e) supplying cooling fluid to said cooling fluid supply chamber, sothat said cooling fluid circulates through heat exchangers of said firsttype of printed circuit cards, and is removed therefrom by way of saidcooling fluid exhaust chamber.
 9. A method according to claim 8, whereinsaid first type of printed circuit cards contain commercial gradeprinted circuit card components having tolerance restrictions less thanprinted circuit card components of VME circuit cards, and wherein saidconductively cooled printed circuit cards comprise VME circuit cards,which are cooled by thermally conducting paths interfacing sides thereofwith said thermally conductive sidewall heat exchangers mounted at saidsidewalls of said chassis.
 10. A method according to claim 8, whereinsaid respective thermally conductive heat exchanger further includes aframe having a first end wall adjoining said fluid supply/exhaust plenumand containing said cooling fluid inlet port and said cooling fluidoutlet port, sidewalls parallel with side edges of said first type ofprinted circuit cards, a second end wall opposite to said first endwall, and a back wall, that enclose first and second adjacent coolingfluid flow chambers, and a further wall that extends from said first endwall to a location spaced apart from said second end wall, so as toprovide an intra chamber fluid communication port connecting said firstand second cooling fluid flow chambers, and a heat exchanger coverplate, and wherein said heat exchanger further includes first and secondthermally conductive heat exchange elements, respectively retained inand substantially filling said first and second cooling fluid flowchambers, but leaving a fluid circulation region therein that provides afluid flow loop path for cooling fluid that has entered said firstchamber via said cooling fluid inlet port in said first end wall of saidframe, and has traveled through said first heat exchange element and,upon exiting said first heat exchange element, travels through saidfluid circulation region and said second heat exchange element in saidsecond chamber, exiting through said cooling fluid exhaust port in saidfirst end wall of said frame.
 11. A method according to claim 8, whereinstep (b) comprises providing gasket material that forms a sealedinterface between said cooling fluid supply and removal slots of saidsupply/exhaust plenum and said cooling fluid inlet and exhaust ports,respectively, of said thermally conductive heat exchangers.
 12. A methodaccording to claim 11, wherein step (b) comprises inserting amulti-apertured gasket inserted between said supply/exhaust plenum andsaid first end wall of said heat exchanger.
 13. A method according toclaim 8, wherein step (a) comprises providing said chassis with acooling fluid inlet that is ported to external ambient and through whichcooling fluid is supplied to said cooling fluid supply/exhaust plenum.14. A method according to claim 13, wherein said sidewalls of saidchassis include respective chambers that are ported to said coolingfluid supply/exhaust plenum at a first portion of said chassis adjacentto a first end of said sidewalls of said chassis, and are ported toexternal ambient at a second portion of said chassis adjacent to asecond end of said sidewalls of said chassis, said respective chamberscontaining thermally conductive heat exchanger elements that arethermally conductively coupled through said chassis sidewalls to saidsecond type of printed circuit cards and over which cooling fluid passesas it travels through said chambers.